1. Field of the Invention
The present invention relates to a CDMA system, and more particularly, to a power linearizer of a CDMA system.
2. Background of the Related Art
In general, a radio frequency band amplifier using active elements generates many undesired distortion components according to a change of a power level.
Especially when the amplifier is operated in the vicinity of a saturation area, a non-linear phenomenon remarkably appears to distort an amplitude and a phase of an output, and when more than two signals are inputted, inter-modulation distortion (MD) components are generated between the input signals, having much influence on the adjacent channel.
The IMD components work as a noise source to degrade a transmission quality of a communication system and reduce a capacity of the CDMA system.
FIG. 1 is a schematic block diagram of a related art power linearizer of a CDMA system. As shown therein, the related art power linearizer includes an input unit 10 for converting a digital input signal (s[n]) into an analog signal(s(t)), a linearization amplifying controller 20 for performing an amplification control to remove a non-linear characteristic of a power amplifier 30, and a power amplifier 30 for amplifying a power of an input signal (s(t)) inputted from the input unit 10 under the control of the linearization amplifying controller 20.
The input unit 10 includes a multiplier 11 for multiplying the digital input signal (s[n]) and a transmission gain signal (g[n]) together, and a digital-to-analog converter 12 for converting the digital signal outputted from the multiplier 11 to an analog signal.
The linearization amplifying controller 20 includes a multiplier 21 for multiplying power control information (c[n]), which controls an increase and decrease of amplification, and a power control step (P) indicative of an increased or decreased power value. It further includes an accumulator 22 for accumulating an output signal of the multiplier 21, an adder 23 for adding a digital output signal of the accumulator 22 and an adjust gain (a[n]) for removing a non-linear characteristic of the power amplifier 30, and a digital-to-analog converter 24 for converting the digital signal outputted from the adder 23 into an amplification control signal of an analog form.
The power control information c[n] has a control value of 1 or 2 in digital form. One control value increases the power as high as a specified value and the other control value decreases the power as low as a specified value. The specified power value refers to the power control step (P).
The multiplier 21 of the linearization amplifying controller 20 multiplies the power control information c[n] and the power control step (P), and the accumulator 22 accumulates the output signal of the multiplier 21.
The adder 23 adds the output signal of the accumulator 22 and the adjust gain (a[n]) and outputs an amplification control signal for controlling amplification of the power amplifier 30 so as to remove a non-linear characteristic of the power amplifier 30. The adjust gain a[n] is a value to adjust the amplification so that the non-linear power amplifier 30 may have a linearity. The value of a[n] used for generating the amplification control signal to remove the non-linear characteristic of the power amplifier 30 is critical.
The digital/analog converter 24 of the linearization amplifying controller 20 converts the output signal of the adder 23 into an analog form, and generates an analog amplification control signal (v(t)) to control an amplification level of the power amplifier 30.
The multiplier 11 of the input unit 10 multiplies the digital input signal (s[n]) and the transmission gain signal (g[n]), and the digital/analog converter 12 of the input unit 10 converts the digital signal outputted from the multiplier 11 into an analog signal s(t) and outputs it to the power amplifier 30.
The power amplifier 30 amplifies the power of the output signal s(t) of the digital/analog converter 12 according to the analog amplification control signal (v(t)) outputted from the digital/analog converter 24 of the linearization amplifying controller 20.
FIG. 2 is a graph showing power characteristic curves of a power linearizer in accordance with the related art amplifier. As shown, PA(V) indicates an actual power characteristic curve of the power amplifier 30, PB(V) indicates a required linear power characteristic curve, and PC(V) indicates a power compensation curve to remove the non-linear characteristic.
In the CDMA system, in order to minimize the influence on the adjacent channel and increase the subscriber accommodation capacity, each mobile terminal should use the minimum power.
With reference to FIG. 2, on the assumption that a desired power is P2, when the power amplifier 30 has a linear characteristic, V1 is to be applied to the power amplifier 30 as a value of the input signal. However, when the voltage of V1 is inputted, the power amplifier 30 outputs a power of P1 according to the non-linear characteristic.
Accordingly, the power of P2 should be obtained through the power compensation. That is, as shown in the output characteristic of the power amplifier 30, an input voltage of V2 is necessary to output the accurate P2.
Thus, the value of V1xcx9cV2 is compensated by using a value of the amplification control signal v(t) of the power amplifier 30, and the value of the adjust gain a[n] used for generating the corresponding amplification control signal v(t) is to be generated.
The value of a[n] is computed by using a difference value between a requested input voltage according to the linearization characteristic curve for outputting a desired power and an actual input voltage according to a nonlinear characteristic curve for outputting the desired power. The conventional power linearizer has the adjust gain a[n], that is, the compensation value for outputting a desired power, in a table form. Accordingly, a value to be compensated at an arbitrary point (an input voltage) is computed by linearly interpolating a corresponding value stored in the table.
The power linearizer of the related art has many problems. For example, the conventional power linearizer should have a slope of a straight line for interpolation and an offset value, and a power compensation value at an arbitrary position of the equation of the straight line should be computed, which makes it complicated to implement the power linearizer.
In addition, the conventional power linearizer compensates the power by adjusting the amplification control signal of the amplifier as much as an error between the linear power (a requested power) and the non-linear power. In this respect, the amplification control signal controls the amplification of the power amplifier in an analog format. Since analog signals are influenced by noise, it is difficult to accurately control the power.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Another object of the present invention is to provide a power linearizer of a CDMA system that is capable of accurately and easily compensating a non-linearity of a voltage controlled power amplifier (VCA).
Another object of the present invention is to provide a power linearizer of a CDMA system that is capable of increasing a capacity of the CDMA system by controlling a digital gain of the VCA.
To achieve at least the above objects in whole or in part and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a power linearizer, including a power amplifier configured to amplify a compensated analog input signal into a control signal, a linearization input circuit coupled to receive a digital input signal and generate the configured to compensated analog input signal to compensate for a non-linear characteristics of the power amplifier, and an amplification controller configured to control an amplification of the power amplifier.
To further achieve at least the above objects in whole or in part and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a power linearizer, including an adder configured to add a gain adjust to compensate for a non-linear characteristic of a voltage controlled power amplifier and a transmission gain signal, and to output a digital gain signal, a multiplier configured to multiply the digital gain signal and a digital input signal to provide a compensated digital input signal, and a digital/analog converter configured to convert the compensated digital input signal into a compensated analog input signal.
To further achieve at least the above objects in whole or in part and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a power linearizing method, including computing an power error value between a linear power (P2) and a nonlinear power (P1) for an input voltage, square root processing the power error value and computing an adjust gain value, adjusting a transmission gain signal using the adjust gain value, ompensating a level of a digital input signal using the adjusted transmission gain signal, and amplifying a power of the level-compensated input signal and outputting a linearized power signal.
To further achieve at least the above objects in whole or in part and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a power linearizer, including means for computing an power error value between a linear power (P2) and a nonlinear power (P1) for an input voltage, means for SQUARE ROOT processing the computed power error value and computing an adjust gain value, means for adjusting a transmission gain signal by using the computed adjust gain value, means for compensating a level of a digital input signal by using the adjusted transmission gain signal, and means for amplifying a power of the level-compensated input signal and outputting a linearized power signal.
To further achieve at least the above objects in whole or in part and in accordance with the purpose of the invention, and embodied and broadly described herein, there is provided a method of compensation a non-linear characteristic of a power amplifier, including adding a digital compensation signal to a digital gain adjust signal to generate an adjusted digital compensation signal, applying the adjusted digital compensation signal to a digital input signal to generate an adjusted digital input signal, and converting the adjusted digital input signal to an adjusted analog input signal.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.